Cindy Hahamovitch is a history professor at the College of William & Mary and the author of “No Man’s Land: Jamaican Guestworkers in America and the Global History of Deportable Labor .”WILLIAMSBURG, Va. — IN 1965, the secretary of labor, Willard Wirtz, stood under a porch light in Belle Glade, Fla., facing a crowd of guest workers from the Caribbean. Mr. Wirtz could smell sweat and burned sugar cane on their clothes but couldn’t see them, which was how the workers wanted it. Guest workers were often deported and blacklisted for striking or simply questioning whether they had been paid what they were owed.“I would hear their voices — they would ask questions,” Mr. Wirtz recalled, but “they weren’t going to be identified.”